Mission controllers for NASA's Mars Polar Lander mission are awaiting the next opportunity to communicate with the spacecraft, whose transmissions have not yet been received since it landed on Mars shortly after noon Pacific time today.

"I'm very confident the lander survived the descent," said Mars Polar Lander Project Manager Richard Cook at JPL. "Everything looked very good. I think we're a long way from getting concerned. It is not unexpected that we would not hear from it during the first opportunity." A variety of hardware problems from which the lander could recover may be responsible for the delay in initial telecommunications.

During the last telecommunications opportunity, which began at 2:04 p.m. PST, the spacecraft would have automatically moved its steerable antenna in a search pattern designed to find the Earth. The next communications window opens at 6:27 p.m. PST today when the team will again send commands to the lander instructing it to maneuver its medium gain antenna in another attempt to look for Earth. The lander would then carry out that procedure to transmit to Earth beginning at 8:08 p.m. until 10:40 p.m. tonight.

Even if no transmissions are heard today mission controllers have another opportunity to hear from the lander on Saturday. This is the time the spacecraft would be transmitting if it went into a safe mode shortly after landing. Engineers would also listen for it on Sunday evening, when the spacecraft would automatically switch to its UHF radio and transmit via Mars Global Surveyor. After that, they will send commands instructing the spacecraft to swap between various hardware subsystems in case one is damaged.

The Deep Space 2 microprobes, which impacted Mars about 60 kilometers (about 35 miles) from the lander, will transmit data through Mars Global Surveyor. The team will be listening tonight at about 7:30 p.m. when contact is expected with the microprobes.

The flight team's best flight path estimates are that lander most likely touched down at about 76.1 degrees south latitude, 195.3 degrees west longitude. The estimates for the Deep Space 2 microprobe impacts are 75.0 degrees south latitude, 163.5 degrees east longitude with the two probes being separated from each other by only a few kilometers.

Mars Polar Lander is part of a series of missions in a long- term program of Mars exploration managed by JPL for NASA's Office of Space Science, Washington, D.C. JPL's industrial partner is Lockheed Martin Astronautics, Denver. JPL is a division of the California Institute of Technology in Pasadena.

NASA's Mars Polar Lander is performing flawlessly and poised to land on the layered terrain near the red planet's south polar region shortly after noon Pacific time today, the mission team reported.

The Mars Polar Lander navigation team reported on the success of this morning's trajectory adjustment, which took place at 5:39 a.m. PST. "It seems to be coming in pretty much right on the target line," said Michael Watkins, manager of JPL's navigation and mission design section.

Flight controllers opted to perform the final trajectory adjustment of the mission early this morning. "It was as smooth and clean a maneuver as we've done," said Project Manager Richard Cook. "We're a gnat's eyelash away from our target."

Wind speeds at NASA's Deep Space Network complex at Goldstone, Calif., were expected to remain in an acceptable range and not force stowage of the large antennas used to receive Polar Lander's signal after landing, Cook said. Winds in the range of about 32 kilometers (20 mph) were reported. The antennas would be stowed if there were sustained winds of about 80 kilometers per hour (50 mph) or gusts from about 73 to 88 kilometers per hour (45-55 mph).

The entry, descent and landing sequence is the most complex and risky part of the mission. During descent, the spacecraft will enter the Martian atmosphere traveling at 6.9 kilometers per second (15,400 miles per hour). Onboard accelerometers will sense when friction from the atmosphere causes the lander to slow. From that time, it will be approximately 5 minutes and 30 seconds until touchdown on the surface, during which time the spacecraft will experience G forces up to 12 times Earth's gravity and the temperature of the heat shield's exterior will rise to 1,650 C (3,000 degrees F).

Based on images from the camera on NASA's Mars Global Surveyor, the landing site, near the south polar layered terrain is expected to be devoid of rocks, generally flat and rolling, and fields of sand or dust dunes may be present, said Polar Lander Project Scientist Dr. Richard Zurek.

The Deep Space 2 microprobes, which are piggybacking on the lander, will be jettisoned to the planet about 5 minutes before the lander enters the Martian atmosphere. They will impact the Martian surface about 60 kilometers (about 35 miles) northwest from spot where Mars Polar Lander will set down. The probes, called Scott and Amundsen after early Antarctic explorers, will hit the Mars surface about 1 kilometer (less than a mile) from each other.

The earliest signal from the spacecraft on Mars would be received at 12:39 p.m. PST, said Cook.

Mars Polar Lander is part of a series of missions in a long- term program of Mars exploration managed by JPL for NASA's Office of Space Science, Washington, D.C. JPL's industrial partner is Lockheed Martin Astronautics, Denver. JPL is a division of the California Institute of Technology in Pasadena.

Mars Polar Lander flight controllers opted to perform the last trajectory adjustment of the mission early this morning, sending commands to the spacecraft that will result in a short engine firing to target the spacecraft to the desired landing site near layered terrain in the red planet's south polar region.

Mars Polar Lander is scheduled to land on Mars shortly after noon Pacific time on Friday, December 3. The first signal is expected to be received at 12:39 p.m. The entry, descent, and landing sequence is the most complex and risky part of the mission.

The engine firing was scheduled for 5:39 a.m. Pacific time for 8 seconds, said flight operations manager Dr. Sam Thurman. "This maneuver will increase the entry flight path angle by 0.25 degrees, moving the flight path from our most recent estimate, 12 hours prior to entry, of minus 13 degrees back to the target value of minus 13.25 degrees," Thurman said. "We decided to perform the maneuver in order to ensure that the entry flight path achieved will be very close to the planned trajectory. It puts is just about right on top of the target point, which is in an area chosen because the terrain provides for a safe touchdown."

During descent, the spacecraft will enter the Martian atmosphere traveling at 6.9 kilometers per second (15,400 miles per hour). Onboard accelerometers will sense when friction from the atmosphere causes the lander to slow. From that time, it will be approximately 5 minutes and 30 seconds until touchdown on the surface, during which time the spacecraft will experience G forces up to 12 times Earth's gravity and the temperature of the heat shield's exterior will rise to 1,650 C (3,000 degrees F).

The Deep Space 2 microprobes, which are piggybacking on the lander, will be jettisoned to the planet about 5 minutes before the lander enters the Martian atmosphere. They will impact the Martian surface about 60 kilometers (about 30 miles) away from spot where Mars Polar Lander will set down.

Mars Polar Lander is part of a series of missions in a long- term program of Mars exploration managed by JPL for NASA's Office of Space Science, Washington, D.C. JPL's industrial partner is Lockheed Martin Astronautics, Denver. JPL is a division of the California Institute of Technology in Pasadena.